1S77.] ^J-7 (Copo. 



brain. Superiorly it presents a large transverse tuberosity, with tlie lateral 

 portions well defined, but not distinguished from the cast of the hemis- 

 pheres on the median line. From its latero-superior prominences it ex- 

 tends downwards and forwards on each side, expanding laterally and nar- 

 rowing as it approaches the inferior surface. Each lateral portion is sepa- 

 rated from the hemisphere by a deep fissure, into which a prominent crest 

 of the lateral cranial walls projects. This crest commences al)ove, nearly 

 at the plane of the superior wall, and curves downwards and forwards to 

 below the middle of the cavity which contained the hemispheres. The 

 inferior face of the middle region of the brain is bounded laterally by 

 the projecting masses above described, posteriorly by the constric,i(>n in 

 front of the medulla, and anteriorly by a slight contraction marking the 

 boundary of the hemispheres. Its anterior lateral angles are continued 

 into a fossa of the cranium, which I did not clear of the matrix, but wliich 

 doubtless gives exit to the foramina sphenoorbitale and mtunduvi. The 

 protuberance which occupies this fossa here, includes the base of the tri- 

 geminus nerve. A short distance posterior to this position on the inferior 

 side of the lateral expansion of the middle brain, is the slight projection 

 which covers the cavities of the /(??"aTOe7i ovale &nd the foramen laccrum 

 posterius. Between these on the middle line, is a pair of longitudinal 

 elevations divided by a median longitudinal depression. Posteriorly 

 they rise from the transverse constriction of the medulla ; anteriorly 

 they terminate rather abruptly, the one half at a point anterior to the 

 other. This assymmetry is found in the osseous basis cranii, and is 

 not due to accident. This median ridge is separated by a wide, shallow 

 concavity from the lateral border on each side. A short distance an- 

 terior to the foramen sphemiorbitah is a small fossa which I have not 

 explored, but which is the opening of iXxe foramen opticnm. Tliey are of 

 small size, indicating a corresponding character for the optic nerve. 



The cerebral hemispheres are relatively and absolutely very small, their 

 median long diameter being one-fifieenlh the total length of the skull, or 

 a little smaller than those of the Uintatherium mirabile, according to the 

 figures and description of Marsh. They are together about as wide as deep 

 posteriorly, but botli diameters diminish rapidly forwards, the vertical the 

 most rapidly. Tlie profile slopes downwards and forwards to the base of 

 tlie broad olfactory peduncles. There are no convolutions nor any decided 

 indication of the Sylvian fissure,* but there are surface-casts of the small 

 arteries that ramified in the dura mater. Owing to the prominence for- 

 wards of the inferior part of the middle brain, but a small part of the in- 

 ferior surface of the hemisi)here is visible. The olfactory lobes are the 

 largest known among Mammalia, and greatly exceed those of Uintatherium, 

 as described by Marsh, and even those of Oxymna. Their peduncle is 

 transversely oval in section, and is directed horizontally forwards for a 



* Prof. Marsh (Amer. Journ. .Sci. Arts, 1876, p. If)6) states that both convolu- 

 tions and a Sylvian fl.ssure are present in Uintatherium. The.'-e assertions are 

 not justified by his figures, nor by the protjably (Similar briiiu of CvryitliodqiK 



